The present invention relates generally to antenna assemblies for wireless communication devices and systems, and in particular to slot antenna assemblies. The invention provides particular utility to slot antennas for use in laptop computers, telecommunications devices, or other wireless devices, and in wireless local area network systems.
There is a growing need for a structurally compact, resonant antenna assembly for efficient operation over a variety of frequency ranges including, for example, the wireless LAN frequencies. A further need exists for such an antenna to be suitable for mounting within a communication device and yet have little or no operational interference from other internal components of the device. In addition, there is a need for such antennas to have robust hemispherical coverage while minimizing external interference.
Existing antenna structures for wireless devices include both external and internal structures. External single or multi-band wire dipole antennas are half wave antennas operating over one or more frequency ranges. The typical gain is +2 dBi. These antennas have no front to back ratio and therefore radiate equally toward and away from the user of the wireless device without Specific Absorption Rate (SAR) reduction. LC (inductor and capacitor) traps may be used to achieve multi-band resonances. The bandwidth near the head is limited to 80 degrees nominal.
Another external antenna structure is a single or multi-band asymmetric wire dipole. This antenna is a quarter wave antenna operating over one or more frequency ranges. The typical gain is +2 dBi. There is no front to back ratio or SAR reduction. LC traps may be used to achieve multi-band resonances. An additional quarter wave conductor is needed to achieve additional resonances. The beamwidth near the head is limited to 80 degrees nominal.
Internal single or multi-band antennas include asymmetric dipole antennas. These antennas include quarter wave resonant conductor traces, which may be located on a planar, printed circuit board. These antennas operate over one or more frequency ranges with a typical gain of +1 to +2 dBi, and have a slight front to back ratio and reduced SAR. These antenna structures may have one or more feedpoints, and require a second conductor for a second band resonance.
Another internal antenna structure is a single or multi-band planar inverted F antenna, or PIFA. These are planar conductors that may be formed by metallized plastics. PIFA operate over a second conductor or a ground plane. The typical gain for such antennas is +1.5 dBi. The front to back ratio and SAR values are dependent of frequency.
An antenna assembly having first and second front panels generally vertically aligned in an orthogonal orientation to one another is described. The front panels include a slot which is continuous across the junction of the front and second panels, so the slot itself is also orthogonal. The orthogonal slot antenna assembly of the present invention is useful in laptop computers or other wireless devices benefiting from a compact and yet robust antenna which radiates with multiple polarizations in various multiple orientations. Additionally, the antenna assembly may be used with such devices with minimal operational interference.
The antenna assembly may also include the following properties: a size suitable for integration within a laptop computer unit, preferably at a front corner of the laptop unit; minimization of operational interference from a laptop docking station or other external sources by placement of the antenna in the preferred front corner of the laptop; minimization of operational interference from internal components of the laptop or other device by providing reflecting panels which may be electrically coupled to a device ground; robust hemispherical coverage achieved by the orthogonal orientation of the front panels and further enhanced by tilting the front panels relative to a horizontal plane; and enhanced performance at selected wireless LAN frequency ranges, preferably 2.4-2.5 GHz.
Another object of the invention is to provide an antenna integrated upon a transceiver board for ease and economy of manufacture. In one embodiment, an improved slot antenna assembly is provided for use with laptop computers, personal data devices, and other wireless communication devices. The antenna assembly is of a compact size suitable for mounting directly on the motherboard of a laptop computer. The orthogonal orientation of the front panels of the antenna optimizes the performance of the antenna within the laptop or other device. The antenna is preferably positioned at a front corner of the laptop computer or other device. The orientation and position of the antenna are designed to provide essentially equal performance with the laptop display open or closed, and to minimize interference from external sources, such as a docking station or a user""s hands on the keyboard.
The orthogonal slot antenna assembly of the present invention also preferably includes reflecting panels between the front panels and other internal components of the laptop. These reflecting panels serve to minimize or eliminate operational interference from these internal components, further enhancing the antenna""s performance.
Other objects and advantages will in part be obvious and will in part appear hereinafter, and will be accomplished by the present invention which provides an omni-directional slot antenna including a circuit board having a first dimension and a second dimension perpendicular to the first dimension. Electronic circuitry which receives and/or transmits RF signals is mounted to the circuit board. Typically, the electronic circuitry will also include an electronic circuit or network to match the impedance between the antenna and the receiving/transmitting circuitry. A first slot antenna arm is parallel to the first dimension and a second slot antenna arm parallel to the second dimension with one end of the first slot antenna arm connected or joined to the second slot antenna arm at a selected location so as to form, for example, a xe2x80x9cLxe2x80x9d shaped slot antenna.
The antenna has a three dimension, omni-directional pattern, able to communicate using vertical and horizontal polarization signals with reasonable gain. The antenna exhibits a three dimension omni directional pattern without using complex structures such as arrays or two slots in a cross pattern. For example, the L-slot antenna is built as two arms orthogonal to each other to direct the current flow path so as to form a three dimension omni-directional radiation pattern. The design requires only a single feed point connecting the transceiver to the antenna, thus greatly simplifying the structure and reducing the cost compared to arrays or cross slot antennas.
In one preferred embodiment, the slot antenna includes an elongate orthogonal aperture. The length and width dimensions of the slot (i.e., the slot perimeter length) determines the resonant frequency of the antenna. By changing the slot perimeter length, the resonant frequency of the antenna can be very accurately adjusted to the desired value.
In another preferred embodiment, the antenna assembly includes top horizontal panels connected to the front panels. These top panels further assist in tuning the antenna to a predetermined resonant frequency.
In another embodiment, the antenna assembly may be disposed away from the ground plane of an associated wireless communications device and coupled via a signal transmission line such as an RF coax line, a microstrip transmission line, a coplanar wave guide, or other known signal transmission approaches as appreciated by those skilled in the arts.
In another embodiment, the antenna assembly of the present invention is further reduced in size by providing a meander slot upon the front panels. By doing so, the overall size of the antenna assembly can be reduced. An additional preferred embodiment includes a second slot in addition to the meander slot in the front panels. The second slot allows shifting of the frequency band for frequency band adjustment.